A coking oven generally comprises a number of coking chambers arranged in row, each of which can be provided on its roof with a riser for carrying away the gases generated during the coking process.
The riser is usually a ceramic-lined steel or iron pipe which can have a length or height of, say, 4-6 meters, comparable in height to the height of the coking chamber.
At its upper end, the riser is provided with a reasonable cover and adjacent its upper end with a lateral fitting for connecting the riser to a subsequent apparatus such as a recuperator for recovering part of the heat generated in the coking process or a gas-cleaning installation. The gas which is generated in the coking chamber, can pass or be drawn by suction through the riser.
Between the fitting and the apparatus a valve or the like is generally provided. The valve can include or be a water trap.
From time to time risers of the aforedescribed type, which accumulate soot, carbon black and heavier deposits of combustible material, must be cleaned to eliminate the cross section reduction caused by such deposits.
In one conventional process for the internal cleaning of such risers, the cover is removed and a weighted cleaning head is dropped through the top of the riser and lowered therethrough. The cleaning head can be raised and lowered repeatedly to effect the desired degree of cleaning.
The cleaning action of the cleaning head can be accomplished by mechanical means, e.g. brushes or blades which physically dislodge the deposits. It is also known to introduce an oxygen lance through the top of the riser and to lower it while directing oxygen against the deposits at a temperature sufficient to cause combustion thereof. In a third cleaning technique, jets of water are directed at extremely high pressure against the deposits to dislodge them. The latter technique is hereinafter referred to as hydraulic and the head as a hydraulic cleaning head.
With all of these conventional processes the cleaning of the riser is problematical since the open upper end of the riser serves as a means for escape of the detritus which is dislodged from the wall of the pipe or gases which are generated by the combustion of such deposits.
In addition, emission from the chamber itself may occur.
The uncontrolled emission of particles and gases during the cleaning process is a severe disadvantage.